Re: [Qemu-devel] [PATCH for-2.9] i386: Don't override -cpu options on -cpu host/max

[Igor Mammedov]

On Fri, 24 Mar 2017 17:36:45 -0300
Eduardo Habkost <address@hidden> wrote:

> The existing code for "host" and "max" CPU models overrides every
> single feature in the CPU object at realize time, even the ones
> that were explicitly enabled or disabled by the user using
> "feat=on" or "feat=off", while features set using +feat/-feat are
> kept.
> 
> This means "-cpu host,+invtsc" works as expected, while
> "-cpu host,invtsc=on" doesn't.
> 
> This was a known bug, already documented in a comment inside
> x86_cpu_expand_features(). What makes this bug worse now is that
> libvirt 3.0.0 and newer now use "feat=on|off" instead of
> +feat/-feat when it detects a QEMU version that supports it (see
> libvirt commit d47db7b16dd5422c7e487c8c8ee5b181a2f9cd66).
> 
> Change the feature property getter/setter to set a
> env->user_features field, to keep track of features that were
> explicitly changed using QOM properties. Then make the
> max_features code not override user features when handling "-cpu
> host" and "-cpu max".
> 
> This will also allow us to remove the plus_features/minus_features
> hack in the future, but I plan to do that after 2.9.0 is
> released.
> 
> Reported-by: Jiri Denemark <address@hidden>
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
>  target/i386/cpu.h |  2 ++
>  target/i386/cpu.c | 33 +++++++++++++++++++++------------
>  2 files changed, 23 insertions(+), 12 deletions(-)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 07401ad9fe..c4602ca80d 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1147,6 +1147,8 @@ typedef struct CPUX86State {
>      uint32_t cpuid_vendor3;
>      uint32_t cpuid_version;
>      FeatureWordArray features;
> +    /* Features that were explicitly enabled/disabled */
> +    FeatureWordArray user_features;
>      uint32_t cpuid_model[12];
>  
>      /* MTRRs */
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 7aa762245a..5f2addbf75 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -3373,15 +3373,20 @@ static void x86_cpu_expand_features(X86CPU *cpu, 
> Error **errp)
>      GList *l;
>      Error *local_err = NULL;
>  
> -    /*TODO: cpu->max_features incorrectly overwrites features
> -     * set using "feat=on|off". Once we fix this, we can convert
> +    /*TODO: Now cpu->max_features doesn't overwrite features
> +     * set using QOM properties, and we can convert
>       * plus_features & minus_features to global properties
>       * inside x86_cpu_parse_featurestr() too.
>       */
>      if (cpu->max_features) {
>          for (w = 0; w < FEATURE_WORDS; w++) {
> -            env->features[w] =
> -                x86_cpu_get_supported_feature_word(w, cpu->migratable);
> +            /* Override only features that weren't not set explicitly
> +             * by the user.
s/not// or if it was intended rephrase to avoid double negation.

> +             */
> +            env->features[w] &= env->user_features[w];
it probably should be assert to catch features not set via property,
which shouldn't be there in the first place, I don't like silent
filtering that happens here.

> +            env->features[w] |=
> +                x86_cpu_get_supported_feature_word(w, cpu->migratable) &
> +                ~env->user_features[w];
>          }
>      }
>  
> @@ -3692,15 +3697,17 @@ static void x86_cpu_unrealizefn(DeviceState *dev, 
> Error **errp)
>  }
>  
>  typedef struct BitProperty {
> -    uint32_t *ptr;
> +    FeatureWord w;
it would be better if this refactoring and related changes
were in a separate patch, something along lines:
 "x86/cpu: use FeatureWord instead of keeping a pointer to cpuid leaf"

>      uint32_t mask;
>  } BitProperty;
>  
>  static void x86_cpu_get_bit_prop(Object *obj, Visitor *v, const char *name,
>                                   void *opaque, Error **errp)
>  {
> +    X86CPU *cpu = X86_CPU(obj);
>      BitProperty *fp = opaque;
> -    bool value = (*fp->ptr & fp->mask) == fp->mask;
> +    uint32_t f = cpu->env.features[fp->w];
> +    bool value = (f & fp->mask) == fp->mask;
>      visit_type_bool(v, name, &value, errp);
>  }
>  
> @@ -3708,6 +3715,7 @@ static void x86_cpu_set_bit_prop(Object *obj, Visitor 
> *v, const char *name,
>                                   void *opaque, Error **errp)
>  {
>      DeviceState *dev = DEVICE(obj);
> +    X86CPU *cpu = X86_CPU(obj);
>      BitProperty *fp = opaque;
>      Error *local_err = NULL;
>      bool value;
> @@ -3724,10 +3732,11 @@ static void x86_cpu_set_bit_prop(Object *obj, Visitor 
> *v, const char *name,
>      }
>  
>      if (value) {
> -        *fp->ptr |= fp->mask;
> +        cpu->env.features[fp->w] |= fp->mask;
>      } else {
> -        *fp->ptr &= ~fp->mask;
> +        cpu->env.features[fp->w] &= ~fp->mask;
>      }
> +    cpu->env.user_features[fp->w] |= fp->mask;
>  }
>  
>  static void x86_cpu_release_bit_prop(Object *obj, const char *name,
> @@ -3745,7 +3754,7 @@ static void x86_cpu_release_bit_prop(Object *obj, const 
> char *name,
>   */
>  static void x86_cpu_register_bit_prop(X86CPU *cpu,
>                                        const char *prop_name,
> -                                      uint32_t *field,
> +                                      FeatureWord w,
>                                        int bitnr)
>  {
>      BitProperty *fp;
> @@ -3755,11 +3764,11 @@ static void x86_cpu_register_bit_prop(X86CPU *cpu,
>      op = object_property_find(OBJECT(cpu), prop_name, NULL);
>      if (op) {
>          fp = op->opaque;
> -        assert(fp->ptr == field);
> +        assert(fp->w == w);
>          fp->mask |= mask;
>      } else {
>          fp = g_new0(BitProperty, 1);
> -        fp->ptr = field;
> +        fp->w = w;
>          fp->mask = mask;
>          object_property_add(OBJECT(cpu), prop_name, "bool",
>                              x86_cpu_get_bit_prop,
> @@ -3787,7 +3796,7 @@ static void x86_cpu_register_feature_bit_props(X86CPU 
> *cpu,
>      /* aliases don't use "|" delimiters anymore, they are registered
>       * manually using object_property_add_alias() */
>      assert(!strchr(name, '|'));
> -    x86_cpu_register_bit_prop(cpu, name, &cpu->env.features[w], bitnr);
> +    x86_cpu_register_bit_prop(cpu, name, w, bitnr);
>  }
>  
>  static GuestPanicInformation *x86_cpu_get_crash_info(CPUState *cs)